This invention relates to flexible magnetic recording disks, popularly known as "floppy disks", of the type used to magnetically store information.
Flexible disk recording media have become an established portable data recording and storage adjunct to a wide variety of computer systems due to the relatively low cost, small size and reliability of individual floppy disks, which affords convenience in storage and handling.
Although originally designed as an approximately 8" diameter flexible disk permanently enclosed in a durable yet pliant envelope with square geometry, recent trends in flexible disk technology have been toward smaller disks. As an example, the 51/4" flexible disk has recently achieved wide popularity for applications in home computers, personal computers, small business computers, and word processing computers.
The most recent trend in the technology of flexible disk media has been toward even smaller diameter disks, and one such disk is the currently emerging 31/4" diameter flexible recording disk, against which there are several competing sizes and designs. One design for a flexible recording disk of this size, generically termed a microfloppy disk, employs a thin flexible recording disk, typically fabricated from three mil Mylar encased in a pliant but durable envelope having an inner bonded liner material. This design closely resembles the original 8" flexible disk and the 51/4" flexible disk, with one important exception. Due to the relatively small dimensions of the microfloppy disk, and the associated disk drive apparatus, it has been found inconvenient to design the disk drive apparatus to accept a microfloppy disk having a rectangular envelope. Rather, due to the drive design characteristics, the envelope must be rectangular in its geometric configuration, thereby having a long axis and a short axis (the length and width dimensions, respectively). This is in contrast to larger flexible disk media assemblies in which the envelope is substantially square.
The use of the rectangular envelope for microfloppy disks creates a problem not encountered with larger sized flexible disks. More particularly, in the larger sized flexible disks having the square envelopes, the perimetral dimensions of the envelope can be chosen in such a manner that the flexible disk confined within the envelope is free to migrate laterally within the enclosure by an equal amount in all radial directions in the plane of the disk: this permits the relatively delicate thin disk to migrate laterally when necessary during insertion of the disk assembly into the associated drive in order to be captured by the hub and spindle clamp assembly, which rotates the disk within the envelope. The amount of radial migration is sufficient to ensure reliable capturing and centering of the flexible disk while still confining such lateral motion to a maximum amount which will not permit the central portion of the flexible disk to be so far off axis from the spindle-clamp assembly to be damaged during the clamping process.
In contrast, in rectangular microfloppy disk assemblies, the rectangular configuration permits substantially more migration of the flexible disk within the envelope in the length direction than in the width direction. Consequently, the flexible disk and metal hub assembly within the envelope is free to migrate to extreme positions along the length direction and are thus much more likely to be mismounted to the drive spindle during the loading process than conventional larger sized flexible disks with square envelopes, absent some mechanism for confining motion of the disk in the length direction. While efforts have been made to solve this problem not present in conventional larger sized flexible disks, the solutions adopted have not been entirely satisfactory. For example, in one such disk motion restricting design, the envelope is fabricated from a moulded plastic material having sufficient wall depth to provide an inner annular recess of preselected diameter forming the inner enclosed volume for the flexible disk. This design suffers from the disadvantages of relatively expensive initial tooling costs, relatively greater materials costs, and nonstandard appearance of the finished disk assembly (as compared to assemblies using the more traditional and conventional durable yet pliant envelope). Other attempts to modify the traditional flexible disk design to provide limit stops for the enclosed flexible disk along the length dimension or direction by adding discrete thin projections extending through the envelope have met with difficulties in providing good bonding with the envelope or jacket material, have added costly additional fabrication steps to the conventional manufacturing process, and have thus not met with wide success. Further attempts to provide the requisite flexible disk limit stop protection in the length direction by stamping projections into the envelope material itself have been altogether unsuccessful, due both to the presence of the inner liner material within the envelope enclosure and the extremely thin dimension of the flexible disk which, when combined with the relatively low friction (i.e., slippery) surface of the disk, facilitates migration of the edge of the disk past staggered opposed protrusions or "bumps" formed in the envelope or jacket surface.